One of the factors which directly affects the driving of a vehicle is the pressure of the tires and, although checking the pressure should be, in principle a simple operation, when the user attempts to carry out the checking he finds a series of problems that in many occasions lead him to give up the attempt as such operation implies loss of time while it also gives rise to getting the users hands dirty, or at best, the user inflates tires untill a value of pressure which he believes to be the correct one, while the appropriate pressure at that particular moment would be different.
The problem for the user when checking the pressure is that he has to obtain the pressure values corresponding to front and rear wheels; however these values vary depending upon whether the tires are cold or warm. As the quantification of these factors is subjective, the user usually chooses an average pressure or a reference pressure value that he considers the most suitable.
At present there are known pressured-air supplying machines on the market, which incorporate a series of push-buttons, each one of which corresponding to a pre-determined pressure value, so that when one of the push-buttons is pressed the machine adjusts the tire pressure to the value assigned to the pressed push-button.
The influence of temperature of the tires on their pressure is important; that is why tire manufacturers recommend an increase of the reference value of 0.3 bar if the pressure is checked when tires are warm. In doing so, the problem of determination of the temperature of the tire comes across, as this temperature may vary more than 50.degree. C. depending upon the environmental temperature and, on the other hand, upon whether the tire has been resting or it has just finished running at a high speed.